The main magnet in an MRI machine is a superconducting solenoid 1.8 m long and 30 cm in radius. During normal operation, the current through the windings is 100 A, the resistance of the windings is zero, and the magnetic field magnitude is 1.5 T. 

(a) What is its inductance? 

(b) The magnet is started by connecting the solenoid to a power supply. It takes 8.0 min for the current to go from zero to 100 A. What is the emf of the power supply?